Hydraulic transmission fluid



United States Patent() 2,731,418 HYDRAULIC TRANSMISSION FLUID William C. Howell, Jr. and Jones I. Wasson, Union, N. J.

assignors to Esso Research and Engineering Company, a corporation of Delaware 3 Claims. (Cl. 252-]42-7) The present invention relates to improvements in hydraulic transmission fluids and more generally to lubrieating compositions having superior anti-friction properties. The invention relates particularly to power transmitting and lubricating compositions designed for use in hydraulic transmissions of modern automotive vehicles.

In the prior art numerous compositions have been proposed for use in torque converters, fluid clutches, semiautomatic and fully automatic automotive transmissions and the like and in some cases difliculty has been encountered in meeting certain specific requirements. This is not surprising when it is considered that for many types of such automatic transmissions the fluid must act not only as a power transmission medium but in addition must provide satisfactory lubrication, actas a hydraulic control fluid, and perform as a heat transfer medium. The fluid must also be free from corrosive effects and objectionable odors. Moreover, the fluid must be so designed as to function properly over a wide temperature range and it must possess a high level of oxidation resistance and a good degree of detergency. The latter properties are extremely, important, since even small quantities of sludge and other oxidation products, if,

allowed to settle out, can easily clog the very small orifices in the hydraulic control system and cause serious malfunctioning and damage to the transmission.

Although many of the numerous compositions of hydraulic transmission fluids hereinbefore referred to have been satisfactory with regard to most .of the requirements as set forth above, .to .date no product has been found that is entirely satisfactory with respect to its anti-friction properties. In one popular type of torque converter transmission,:for example, under certain operating conditions there is sliding contact between certain elements and a tendency for them to alternately seize and separate with stick-slip or chattering, action. Ordinary lubricants such as straight mineral oil and a number of products especiallycompounded for the purpose do not prevent this objectionable type of operation. For example, the lubricants specifically recommended by the manufacturer of this transmission, known as Automatic Transmission Fluids, Type A, are completely inadequate for preventing this chattering action. This is true despite the fact that these approved fluids vary widely in their compositions and contain a widevar'iety of detergent inhibitor additives, anti-friction additives, andother materials. However, when the fluids described in this invention are used, the objectionable chatter, particularly common when certain transmissions are operated in reverse, is almost completely eliminated.

As has been previously mentioned, lubricants for use in automatic hydraulic transmissions must, in addition to other important properties, possess ahigh degree of detergency, freedom from corrosion, and good odor. According to the present invention, it has been discovered that a particular combination of detergent inhibitors and acidic type materials, when combined in the correct proportions, give a fluid that has these desirable long chain fatty acids, or natural fats containing acids of this type (such as lard oil), may be used as anti-friction agents where detergent-inhibitors such as P285 treated barium salt of diisobutyl phenol sulfide are employed.

Even better anti-friction properties can be obtained by theinclusion of certain phosphoric acid esters, especially triphosphate esters such as tricresyl phosphate, along with the acid type anti-friction agent. Saturated long chain fatty acids such as stearic acid or alkyl mercapto acids such as lauryl mercaptoacetic acid cannot be employed with detergent-inhibitors of this type. By substituting an unsaturated acid such as oleic acid, or lard oil, HzS evolution is reduced, probably by being taken up at the unsaturated bonds. When saturated acids are employed,

HzS evolution occurs, resulting in objectionable odor and corrosion properties despite the fact that good antifriction action is obtained. Also, substitution of a non- P2S5 treated detergent-inhibitor such as the barium salt of diisobutyl phenol sulfide for the PzSs-treated detergent material would reduce HzS evolution. However, such substitution cannot be made without destroying the effectiveness of the anti-friction agent. Neither can deter? gent-inhibitors containing petroleum sulfonates be employed for the same reason.

For improved anti-corrosion properties, combined with better detergency and better odor than is obtained with oleic acid-PzSs-treated detergent type blends, it is preferred to use non-Pzss-treated detergent inhibitors. However, neither the saturated or unsaturated fatty acids nor the mercapto acids are effective anti-friction agents in the presence of these non-PzS5-treated detergentinhibitors. It has been discovered, and is another feature of this invention, that if certain concentrations of fatty acid and alkylmercapto acid are employed jointly, excel; lent anti-friction properties result even in the presence of the non-PzSs-treated detergent-inhibitors. Also, very good odor and corrosion properties are observed for blends of this type because of absence of free HzS. Sulfonatecontaining detergent-inhibitors cannot be used, however, without destroying the anti-friction properties.

The invention will be more fully understood by specific reference to a series of blends which have been made in the study of the anti-friction problem. types of detergents were employed. One of these was a highly successful commercial product obtained by treating the barium and/or calcium salt of diisobutyl phenol sulfide with a phosphorus sulfide such as P285. The other consists of the untreated barium or mixed bariumcalcium salt of diisobutyl phenol sulfide. The former gives superior anti-friction properties in combination with fatty acids but has an objectionable tendency to evolve HzS gas under certain conditions. The untreated salt, on

the other hand, is free from the objectionable HzS evolu tion but is somewhat deficient alone or in combination is found to possess all the desired properties to an excellent degree. In the mercapto acids, instead of lauryl the alkyl group obviously may be octyl, 2-ethyl hexyl, decyl, tetradecyl, etc. Among the C12 to C22 fatty acids that may be used are myristic, palmitic, stearic, erucic, bras- In either case the addition of a small amount of tricresyl phosphate serves to improve anti-friction sldic, etc.

properties slightly further.

The preferred embodiments of this invention may be Patented Jan. 17, 1956 In general, two

3 summarized as follows wherethe detergent-inhibitor A represents the type which is free from HzS evolution, such as non-Pz Ss-treatcdbarium or calcium salt of alkyl phenol sulfides, and-type B represents the type which is subject t'o H25 evolution because of prior treatment with a phosphorus'sulfide.

.May beomitted at the expense, oteslight impairment of. anti-friction properties;

A series. of. tests wasmadeof various compositions in.

an actual hydraulic transmission of the torque converter type. where a strong tendency, to. chatter was found in reverse gear. operation. usedQthere. is aLlarge steel bearing surface in the reverse planetary gear setwhich-rotates against abronze bushing when theunit is put into reverse. cated by the. transmission fluid. As will be seen by reference to. the data in Table I,wheneither straight mineral oil or the fluidspresently approved bythemanufacturer of this transmission are used, stick-slip occurs inthis bearing, and undesirable chatter is obtained.

When the fluids described inthisinvention are used, the

chatter is almost entirely eliminated.

Table I Fluid. Torque Converter Reverse Chatter- AHtl-rFIIOtlOH Agent Deten-Inhibitor Approved Type Afluids Medium to Heavy. Straight mineraloil";. Heavy. 0.3%.Stearic acid None 'Veillyht Light to 0.3% Oleie acid. Medium to Heavy.

g. 0.8% Oleic acid. Verg Light. 7

. 0.8% Oleic.acld Lig t. 0.3% Stearic aoi Light (Objection- 7 I able Odor). 0.3% Stearic acid 2.0% Detergent A Medium to Heavy. 0.2% Lauryl mereapto do Do.

acetieacid. Y 10. 0.3% Stearic acid, 0.2% do Very Lt. to Light.

Lauryl mercapto acetic acid. 11. No. 10+0.5 Tricresyl.

phospha L Very Light. 12. 0.4% Stearic acid, 0.5%.

Tricresyl'phosphate..... 2.0% Detergent A Medium to Heavy. 13. 0.3%" Lauryl mercapto acetic acid, 0.5% Tricresyl, phosphate. .do Do.

14. 0.2% Lauryl mercapto aceticacid,0.3%-Stearic acid (2.0% Detergent A, Light to Medium.

1.2% Calcium sulfonate concentrate. l5. 2.0%-N0..1.Lard Oil 2.0%Detergent Btu; Light.

Recommended by manufacturer-for use in thistransmission.

concentrations are objectionable from the. standpoint of.

oxidation stability and corrosion. If. tricresyl phosphateis weight hasbeen found to be effective. Of. those. listed;

In the. particular transmission This bearing is: lubri-- ia edt e's nq it ia io of. out y- In general, the best concentration range for the above in Table I, compositions Nos. 6, 10, Hand 15 are most satisfactory over-all.

In general, the invention contemplates the use of a lubricating oil as a major component. This is preferably a mineral base lubricating oil, although synthetic oils such as dibasic acid esters, complex esters, polyglycols, and the like may be used so long as they are compatible with the additives. The preferred viscosity range is between 35"and 65. S. S. U. at 210 F., particularly between 45 and 55'f0r the average transmission unit.

This lubricating oil base should contain about 1 to 6% by weight, based on the total. composition, of an alkaline earth metal salt of alkyl phenol sulfide as a detergent, which is free from HzS evolution together with 0.2 to 1% by weight of fatty acid of the C12 to C22 range, 0.2 to 0.5% by weight of C8 to C18 alkyl mercapto acid, preferably. analkyL mercapto. acetic acid, and 0 to 1% by 'weight, preferably at. least. 0.2%,. of. a tri-ester of phosphonic acid;cl gt'tricresyl phosphate, as an oiliness agent. Whenimineral oil is used as the fluidbase it preferably'has a viscosity-between 35 and. 65 S'. S. U. at- 210 F. andis of reasonably. high viscosity index. A preferred com- 'positioncornpriscs. 93.7 to. 97.4% of sucha mineral base oilwith 2 to. 6'%} of the. alkaline earth salt of non-P285- treated alkyl phenol sulfide as detergent, 0.3 to 1%. of a fatty acid, preferably a C18 acid, stearic acid being first choice, 0.1 to 0.3% oflauryl mercapto acetic acid although other alkyl derivatives may be used, and 0.2 to 1% of tri cresyl phosphate.

It is to be noted that the invention as described con! templates the use of alkaline earth metal salts derived from thelalkyl' phenol sulfides. asthe preferred detergents,

and that the exact.detergentrinhibitor to be employed will depend upon the nature of the acidic type anti-friction portion of a liquid lubricating oilbase, 1 to 6% by weight,

based on. the total composition of an H2 S free alkaline earth metal saltof alkyl phenol sulfide as a detergent, 0.2, to 1% of fatty acid of the C12 to 022 range, and 0.2 to 0.5% of Ca tO C2 ga1kyl mercapto acetic acid.

2. Composition. according toclaim 1. towhich is. added 0.2 to 1% of. a triester of phosphoric acidas oiliness agent.

3. A hydraulic transmission oilhaving approximately the following compositionby weight:

92.5 to. 98.6% lubricating oil base: of'35 to 65 S. S. U.

vis. at 210 F.

2 to. 5% alkaline earth; metalv salt of diisobutyl phenol sulfide 0.3: to. 1%. Cm fatty. acid.

0.2;to; 0.5 laurylfmercapto acetic acid 0.2 to 1.0%:tricresyl phosphate.

References Cited in thefile of this patent UNITED STATES PATENTS 2,203,102 Powers June 4, 1940 2,409,686 McNab Oct. 22, 1946 2,451,345 McNab-et a1 Oct. 12, 1948 2,474,604, Wassonetal a June 28, 1949 2,5 164.19; Hershly 25, 1950 2,528,347 Denis'on Oct. 31, 1950' 

1. A LUBRICANT COMPOSITION OF HIGH DETERGENCY AND SUPERIOR ANTI-FRICTION PROPERTIES, COMPRISING A MAJOR PROPORTION OF A LIQUID LUBRICATING OIL BASE, 1 TO 6% BY WEIGHT, BASED ON THE TOTAL COMPOSITION OF AN H2S FREE ALKALINE EARTH METAL SALT OF ALKYL PHENOL SULFIDE AS A DETERGENT, 0.2 TO 1% OF FATTY ACID OF THE C12 TO C22 RANGE, AND 0.2 TO 0.5% OF C8 TO C24 ALKYL MERCAPTO ACETIC ACID. 